Phase behavior and chemical compositions of borehole fluids may be utilized to assist in estimating the viability of oil and gas reservoirs. For example, the concentration of gaseous components such as carbon dioxide, hydrogen sulfide and nitrogen in borehole fluids may be indicators of the economic viability of oil and gas reservoirs. The concentrations of various gases may be of interest for different reasons. For example, carbon dioxide corrosion (CO2) and hydrogen sulfide (H2S) stress cracking of downhole tubulars, such as, for example, casing and/or production tubing may be causes of mechanical failure in a borehole environment.
Although a variety of techniques and equipment may be available for performing fluid analysis in a laboratory, retrieving samples for laboratory analysis may be time consuming. Further, some characteristics of borehole fluids may change when brought to the surface due to differences in environmental conditions between a borehole and the surface. For example, because H2S gas may form non-volatile and insoluble metal sulfides by reacting with metals and metal oxides, analysis of a fluid sample retrieved with a metallic container may result in an inaccurate estimate of sulfide content. Fluid analysis techniques that may be utilized at the surface may be impractical in the borehole environment due to borehole size limitations, extreme temperature, extreme pressure, and/or a presence of water. Additionally, an isolation of gases from a borehole fluid may be difficult to achieve.
The presence of an inorganic gas, such as, for example nitrogen, may be highly prevalent in some oil and gas reservoirs. Due to its difficulty to remove from a gas stream in processing, the presence of nitrogen may significantly lower the value of hydrocarbon assets. Nitrogen may not be optically active (e.g., physical visibility or infrared visibility), making conventional downhole detection utilizing downhole methods difficult. Therefore, it may be desirable to determine the content of certain gases, such as, for example, nitrogen in gas reservoirs without the need to recover a sample to the surface in order to complete optimal zones as quickly as possible and as efficiently as possible. Therefore, downhole detection of inorganic gas content, such as nitrogen content, in hydrocarbon reservoirs is desirable.